Solvent extraction of hydrocarbon oil



Patented June 12, 1934 UNITED STATES PATENT OFFICE William M. Stratford, New York, N. Y., assignor to The Texas Company, New York, N. Y-, a corporation of Delaware No Drawing. Application September 28, 1932, Serial No. 635,234

4 Claims.

This invention relates to a process for extracting petroleum hydrocarbons with a selective solvent and more particularly relates to a process Cof efiecting the removal of those hydrocarbons which tend to lower the viscosity index of a hydrocarbon lubricating oil. The invention is directed especially to the process of extracting hydrocarbon lubricating "oils with trimethylene.

It has been found that the hydrocarbons which tend to lower the viscosity index of a hydrocarbon lubricating oil are soluble in trimethylene and, by extracting the oil with trimethylene, these hydrocarbons may be removed by the solvent and separated from the remaining oil, thereby producing a lubricating oil having a high viscosity index, a

low sulfur content and having extreme resistance to oxidation.

It is well known that petroleum products generally contain four groups or types of hydrocarbons, namely, parafiins, naphthenes, aromatics and unsaturates. Of these, the paraffins are the least reactive and the aromatics and unsaturates the most reactive, the naphthenes occupying intermediate positions in the ascending order of reactivity.

This ascending order of reactivity is believed also to be parallel by the decrease of polarity of the four enumerated types of hydrocarbons. The paraffins are considered to be strictly non-polar 50 while the naphthenes, aromatics and unsaturates are polar. It is known that the solubilities in polar solvents of the four groups of hydrocarbons vary directly as. their polarities so that the paraffins are the least soluble in polar solvents and the unsaturates and aromatics the most soluble.

Trimethylene, which is a three-sided carbon ring structure, is an extremely polar compound due, no doubt, to the distortion of the valency bonds. In view of the highly polar character of trimethylene, it is quite miscible with the polar hydrocarbons present in petroleum oils. It does not, however, exert any marked solvent action on the non-polar hydrocarbons. Therefore, by extracting petroleum hydrocarbons with liquid trimethylene under suitable conditions of temperature and pressure, it is possible to bring about the solution of the undesirable hydrocarbons and in this way to effect the concentration and separation of those hydrocarbons having high viscosity indices.

Under normal conditions of temperature and pressure, trimethylene is a gaseous material, its boiling point being 34.4 C. under ordinary atmospheric pressure. However, it may be readily liquefied at from 70 to 85 lbs. of pressure at ordinary atmospheric temperatures. These characteristics of trimethylene are highly desirable in that it may be readily and completely removed from the hydrocarbons which have been extracted with it and the hydrocarbons which it has dissolved. Since the pressures necessary for liquefaction are not exceedingly high, the appa ratus within which the extracting operations are carried out need not be of a massive construction.

Trimethylene has no decided aflfinity for water and therefore any water which may be present in the system willgravitate to the bottom of the system from which it may be withdrawn. Trimethylene also has the advantage of being noncorrosive. For this reason, special liners and alloys are not necessary in the construction of the apparatus in which it is used.

In accordance with my invention, a lubricating oil distillate containing undesirable hydrocarbons of low viscosity index may be extracted with trimethylene whereby the undesirable hydrocarbons are removed and the product is a substantially paraflinic lubricating oil. The procedure may be as follows: A lubricating oil distillate which may or may not have received prior treatment with sulfuric acid or other refining agent, is mixed in any suitable manner with a given volume of liquid trimethylene. The volume of the solvent depends upon the quantity of undesirable compounds which it is desired to remove, although it is the usual practice to use equal volumes of lubricating oil distillate and liquid trimethylene. These are agitated in a suitable manner in a pres- U sure extraction apparatus under such a pressure as to maintain the trimethylene substantially in the liquid state. In certain types of operation it may be desirable to decrease the pressure in order to bring about the evaporation of a certain quantity of trimethylene in order to cool the mixture of lubricating oil distillate and extractant. Any trimethylene so evaporated may be conducted to a suitable liquefaction apparatus where it is compressed in order to return it to the liquid state.

The mixture of lubricating oil distillate and solvent having been brought to the proper temperature, is then allowed to remain quiescent until there is a substantial separation into two layers. The upper layer will consist of the paraffinic hydrocarbons together with a small quantity of liquid trimethylene, while the lower layer will be trimethylene having in solution the polar or low viscosity index hydrocarbons extracted from the lubricating oil distillate.

The two layers are then separated and separately subjected to reductions in pressure whereby the trimethylene is distilled ofl" from the corresponding hydrocarbons. It may be necessary to warm the hydrocarbons to a certain slight extent in order to bring about the complete distillation of the trimethylene. The evolved vapors of trimethylene are conducted to the aforementioned liquefaction apparatus where it may be compressed and returned to the liquid state.

In those cases where lubricating oil distillate contains high proportions of undesirable polar compounds, it may be possible to only partly purify and separate the paraflinic hydrocarbons in one extraction. It may therefore be necessary to treat the extracted oil produced in the first treating step with further quantities of solvent. This is most efficiently accomplished by using the counter-current system of treating in which counter-currently flowing streams of the untreated lubricating oil distillate and trimethylene are alternately mixed together and separated. In such a system the relatively spent trimethylene comes into contact with untreated oil while the relatively finished lubricating oil comes into contact with fresh trimethylene.

Although it is usual practice to treat the lubricating oil distillate with trimethylene at ordinary temperatures, it is possible to make the action of the solvent more specific and selective by carrying out the extraction at relatively low temperatures. However, it is usually not advisable to carry out the extraction at a temperature below the pour point of the oil although this may be successfully accomplished by using relatively large volumes of solvent.

Obviously many modifications and variations of theinvention, as hereinbefore set forth, may be made Without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. The method of producing a lubricating oil of high viscosity index from a lubricating oil distillate which comprises mixing and agitating the distillate with liquid trimethylene under such conditions of temperature and pressure as to maintain it in the liquid state, allowing the mixture to remain undisturbed in order to effect stratification, drawing off the supernatant layer of treated oil and a relatively small amount of trimethylene, and separating said trimethylene from the treated oil by distillation.

2. In the treatment of petroleum oils containing polar and non-polar hydrocarbons, the method of separating the polar from the non-polar hydrocarbons which comprises extracting the petroleum oil with liquid trimethylene whereby the polar hydrocarbons become dissolved therein, and separating the non-polar hydrocarbons from the solution of polar hydrocarbons in trimethylene.

3. The method of producing a lubricating oil of high viscosity index from a lubricating oil distillate which comprises mixing and agitating the distillate with liquid trimethylene under such conditions of temperature and pressure as to maintain the trimethylene in the liquid state, allowing the mixture to remain undisturbed in order to effect stratification, removing the lower layer composed of low viscosity index constituents and further treating the upper layer with further quantities of trimethylene.

4.1m the method of preparing lubricating oil of high viscosity index from mineral oil by treating with liquid trimethylene, chilling and forming an upper and lower layer, the method of cooling the mixture comprising evaporating a portion of the trimethylene from the mixture with refrigerative effect.

WILLIAM M. STRATFORD. 

